This invention relates to an uncoated woven fabric, which comprises a woven fabric, ideal for use in an air bag for vehicles or the like, as well as a method of manufacturing the uncoated woven fabric.
An air bag device provided on a stationary portion of the vehicle body of an automobile in front of a seat of the automobile has an air bag inflated instantaneously by the pressure of a reaction gas emitted by an inflator secured to the steering wheel or dashboard, thereby protecting a seated passenger from injury caused by a vehicular collision. Thus, the air bag device performs a very important function.
The shape of the air bag in such an air bag device differs depending upon the location at which the air bag is mounted. For example, as shown in FIG. 6, an air bag 1 for the driver's seat comprises a substantially circular bag body having a disk-shaped base fabric 1a attached to a fixed portion of the vehicle body, such as the steering wheel, and a circular base fabric 1b facing the driver. The base fabrics 1a, 1b are superimposed and sewn together at A along their circumferential edges and turned over. The air bag 1 has an opening 2 provided in the base fabric 1a, which is secured to the vehicle body, into which the inflator (not shown) that generates the reaction gas is inserted. The air bag 1 is further provided with vent holes 3 from which the reaction gas is discharged after the driver is impacted against the air bag 1.
As shown in FIG. 7, a passenger air bag 4 is provided in the instrument panel and has a complicated shape owing to the fact that the space between the assistant driver's seat and the instrument panel is large. The passenger air bag 4 includes a front panel 4a, a rear panel 4b and a pair of side panels 4c, 4d. The edges of these panels are overlapped and sewn together and turned over to form the air bag 4.
In general, the driver and passenger air bags 1, 4 both consist of a synthetic resin such as polyimide resin and are formed from a suitable number of base fabrics in which a thin coating film 5 (shown only on the driver's air bag 1 in FIG. 6) of chloroprene rubber or silicone rubber is provided on the inner surface. By providing the thin coating film on the inner surface of the base fabric, the base fabric is protected from the high temperature and high pressure of the reaction gas jetted from the inflator when the air bag is inflated.
In order to lighten the air bag device and make it more compact, there has recently been greater demand for an air bag base fabric that can lighten the air bag and reduce the volume of the package. Since progress has been made in lowering the temperature of the reaction gas by virtue of an improvement in the performance of the inflator and the development of aspirator-type air bag devices, air bags which use a fabric on which a thin coating film is not formed (such a fabric shall also be referred to as an "uncoated fabric" hereinafter) have become the focus of interest. Since the uncoated fabric does not have a thin coating film such as chloroprene rubber or silicone rubber formed thereon, the thickness of the base fabric is reduced by an amount equivalent to the thickness of the thin coating film, and therefore the air bag is reduced in both weight and package volume.
In a case where an uncoated woven fabric is used, there are occasions where the threads of the uncoated woven fabric become frayed or tattered when the fabric is subjected to cutting. In general, when such an uncoated woven fabric is subjected to a heat-resistance aging test in which it is maintained at a temperature of 80.degree..about.120.degree. C. for 600.about.1000 hrs, the threads becomes ball shaped owing to contraction of the threads and locations are produced where the spaces between threads widen and other locations where the spaces become small. As a result, there are instances where there is a change in properties, such as a change in the amount of air permeability of the base fabric.